The present invention relates to a compact camera provided with automatic focusing function (hereinafter, referred to as "AF"), automatic exposure function for automatically controlling exposure aperture and exposure time interval of a shutter (hereinafter, referred to as "AE") and zooming function for effecting zooming according to a distance from an object, and more specifically relates to adjustment of the shutter aperture size.
The conventional compact camera of the above noted type is provided with an actuator such as electromagnetic actuator of the moving magnet type and stepping motor for generating bidirectionally a driving torque effective to carry out continuous open and close driving of a shutter blade. The driving torque is transmitted through an operating mechanism to the blade to effect AE. The conventional camera is also provided with a zooming mechanism separately from the AE mechanism.
However, in the conventional camera having the zoom lens system with the lens shutter, the lens aperture size or lens stop diameter is held constant without regard to change of focal distance by zooming so as to eliminate complicated aperture size control. However, since F number is determined by F=aperture size/focal distance, F number is considerably varied between short focal distance state and long focal distance state in a lens system having great zoom ratio when the aperture size is held constant. In view of recent trend of the market, the lens system has small F number in the long focal distance state in order to obtain bright condition. Therefore, the lens system has a significantly great aperture size in the short focal distance state, thereby adversely hindering quality of image reproduction. Accordingly, freedom of the lens system design is limited so that a number of lens pieces may be added or nonproductive shape and strict accuracy may be required to ensure a desired performance, thereby affecting size of camera and production cost. Further, if not using such highly sophisticated lens system, there is caused drawback that a desired quality of the photographic image cannot be obtained because the aperture size is not adjusted according to the change of focal distance in addition to the above noted reason.